The ESMRY file can be updated with more time step data in the time span between opening an ESMRY file
and loading actual summary data from the file. This can happen if the ESMRY is generated by an active
run. Length of summary vectors extracted will be equal to number of time steps on disk when the file was
first opened (with the constructor).
this means getting rid of the Opm::filesystem namespace
and directly using std::filesystem, as well as dropping
some of the compat code for the tr filesystem.
we still need the FileSystem.hpp/cpp files though as unique_path
is not part of std::filesystem.
